1. Field of the Invention
The present invention relates to a recording medium used for ink jet recording methods, thermosensitive recording methods, pressure sensitive recording methods, photosensitive recording methods and transfer recording methods, and particularly for ink jet recording methods. In particular, the invention relates to a recording medium that is excellent in ink receptivity, glossiness and light fastness, while having little bleeding and color fading over time in an image portion.
2. Description of the Related Art
Various information processing systems have been developed in recent years along with rapid progress in information technology industries, and recording methods and recording apparatuses suitable for these information processing systems have been developed for practical uses.
Examples of such practically used recording methods include electrophotographic methods, ink jet recording methods, thermosensitive recording methods, pressure sensitive recording methods and thermal transfer recording methods in addition to silver salt photographic recording methods. A high quality image with a sharp image and clear color is required in any of the recording methods described above.
Among these recording methods, the ink jet recording method has been widely used in offices as well as in homes, since this method is advantageous in that it can be used to record on various recording materials, in that hardware (apparatus) therefor is inexpensive and compact, and in that the method is very quiet.
Since resolution of ink jet printers has increased in recent years, obtaining “photorealistic” high quality recorded materials has become possible, and various kinds of ink jet recording sheets have been developed along with such improvement in hardware (apparatus).
Required characteristics for these ink jet printing sheets are generally: (1) rapid drying (rapid ink-absorption speed), (2) proper and uniform diameter of ink dots (no bleeding), (3) good granularity, (4) high circularity of dots, (5) high color density, (6) high chroma (free of dullness), (7) good water resistance, light fastness and ozone resistance of printed portions, (8) high brightness of recording sheets, (9) good storability of recording sheets (no yellowing or bleeding of images in long term storage (excellent in prevention of bleeding over time), (10) substantially no deformation with good dimensional stability (sufficiently small curling), and (11) good running property of hardware.
In the use of photographic glossy paper sheets used for obtaining photorealistic high quality printed material, in addition to the various aforementioned characteristics, the recording sheets are also required to have glossiness, glossiness of printed portions, surface smoothness and texture of printed paper sheets resembling that of silver salt photographs.
An ink jet recording medium having a porous structure in an ink receiving layer has been developed and practically used in recent years for improving the various characteristics described above. Such an ink jet recording medium is excellent in ink receptivity (instantaneous drying ability) while having high glossiness, due to providing the porous structure.
An ink jet recording medium comprising fine inorganic pigment particles and a water soluble resin as well as an ink receiving layer having a high void ratio provided on a substrate has been proposed (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. 10-119423 and 10-217601).
These recording sheets, and particularly an ink jet recording medium having the ink receiving layer comprising a porous structure using silica as fine inorganic pigment particles, are excellent in ink absorbing property due to their construction. Accordingly, the ink jet recording medium has excellent ink absorptivity and a high ink receptivity capable of forming a high resolution image, while the medium exhibits high glossiness.
However, the recording medium has a large oxygen permeability due to its porous coated layer, and deterioration of components in the ink receiving layer may be accelerated. Furthermore, image bleeding over time may occur in accordance with adsorption of moisture on the silica surface.
Small amounts of gases in the air, particularly ozone, cause color fading of a recorded image over time. Since the recording material comprising the ink receiving layer having the porous structure contains many voids, the recorded image is readily faded with the ozone gas in the air. Consequently, fastness against ozone in the air (ozone resistance) is a crucial characteristic for the recording material having the ink receiving layer of the porous structure.
Recording materials in which sulfur-containing compounds such as anti-color fading agents are added in the ink receiving layer for improving various characteristics have been frequently reported.
For example, JP-A Nos. 64-36479 and 1-115677 have proposed ink jet recording media containing thioether compounds.
However, the compounds exemplified in JP-A Nos. 64-36479 and 1-115677 are hydrophobic low-molecular weight compounds and therefore are water insoluble. Accordingly, it is difficult to mix the compounds with coating liquids, and glossiness of the ink jet recording medium is deteriorated even when these compounds are added as emulsions.
JP-A Nos. 2002-86904 and 2002-36717 have proposed to use thioether compounds having hydrophilic groups.
However, while the compounds exemplified in JP-A Nos. 2002-86904 and 2002-36717 exhibit ozone resistance, bleeding over time becomes worse under high-temperature/high-humidity conditions since the compounds are hydrophilic low-molecular weight compounds. Moreover, since most of such compounds have low melting points, there has also been a problem in that the thioether compound is precipitated on the surface of the recording sheet when stored in a low temperature environment at, for example, 5° C. or lower for one week.
Although polysulfide compounds (disulfide and trisulfide compounds with a molecular weight of less than 1,000) have been used, for example, in JP-A No. 2001-315432, these compounds do not exhibit a sufficient effect for enhancing ozone resistance.
JP-A Nos. 11-58941 and 63-260477 have proposed polymer compounds containing thioether bonds.
However, the ozone resistance improving effect of the compounds exemplified in JP-A Nos. 11-58941 and 63-260477 (and similar compounds) is also insufficient since the sulfur content is low (1 meq/g or less) in the polymer.
JP-A Nos. 11-268406 and 2001-270227 have proposed cationic polyaddition polymers synthesized using specific thioethers.
However, although water resistance is improved by adding the cationic polyaddition polymers in the ink receiving layer, ozone resistance is still insufficient.
JP-A No. 2003-54118 has proposed specific polymer compounds.
However, since the polymer compounds described in JP-A No. 2003-54118 are formed into organic particles having Tg of 70° C. or more, glossiness of the layer is decreased.